U.S. Pat. No. 5,135,785 describes films consisting of a polyethylene or polypropylene layer between two layers of an ethylene/vinyl acetate (EVA) copolymer containing at least 18% by weight of acetate. These films may be welded to make flexible sachets. These films have a permeability to oxygen; indeed, when the sachets contain concentrated bleach, decomposition of the bleach takes place over time with evolution of oxygen. If this oxygen is not released, the flexible sachet may split. These films are also permeable to fragrances. The prior art presents this loss of fragrances to the outside of the sachet as being necessary to allow the user to identify the product in the flexible sachet.
The loss of fragrance should not exceed 15% in 90 days of storage of the sachet. This is all merely a desired situation, the prior art includes no examples. Indeed the Applicant has found that the loss of fragrance was such that after 30 days the sachet no longer had any odour, although it originally contained large amounts of fragrance. The EVA must also contain slip agents, but exactly which they are is not stated and the film can only be welded within a period of from 4 to 20 weeks of its manufacture.
EP 477,025 has also described such multilayers, which consist of a polymer barrier between two layers of EVA or of ethylene/alkyl (meth)acrylate copolymer. The polymer barrier may be a linear low-density polyethylene (LLDPE), a polyamide-polyethylene (PE) bilayer, an EVOH-polyethylene bilayer and preferably a polyamide or an EVOH between two layers of polyethylene (EVOH denotes a copolymer of ethylene and of vinyl alcohol, also known as hydrolysed EVA); that is to say that the films of the prior art may consist, for example, of the following layers:
EVA/PE/PA/PE/EVA or EVA/PE/EVOH/PE/EVA PA1 of one or more amino acids, such as aminocaproic acid, 7-aminoheptanoic acid, 11-aminoundecanoic acid and 12-aminododecanoic acid of one or more lactams such as caprolactam, oenantholactam and lauryllactam; PA1 of one or more salts or mixtures of diamines such as hexamethylenediamine, dodecamethylenediamine, meta-xylylenediamine, bis-p-aminocyclohexylmethane and trimethylhexamethylenediamine with diacids such as isophthalic acid, terephthalic acid, adipic acid, azelaic acid, suberic acid, sebacic acid and dodecanedicarboxylic acid; PA1 or mixtures of some of these monomers which lead to copolyamides, for example PA-6/12 obtained by condensation of caprolactam and lauryllactam. PA1 polyethylene, polypropylene, copolymers of ethylene with alpha-olefins, it being possible for these products to be grafted with unsaturated carboxylic acid anhydrides such as maleic anhydride or unsaturated epoxides such a glycidyl methacrylate. PA1 copolymers of ethylene with at least one product chosen from (i) unsaturated carboxylic acids, their salts and their esters, (ii) vinyl esters of saturated carboxylic acids, (iii) unsaturated dicarboxylic acids, their salts, their esters, their hemiesters and their anhydrides, and (iv) unsaturated epoxides. PA1 styrene/ethylene-butene/styrene (SEBS) block copolymers which are optionally maleic-treated. PA1 polyethylene, PA1 copolymers of ethylene and of an alpha-olefin, PA1 copolymers of ethylene/an alkyl (meth)acrylate, PA1 copolymers of ethylene/an alkyl (meth)acrylate/maleic anhydride, the maleic anhydride being grafted or copolymerized, PA1 copolymers of ethylene/an alkyl (meth)acrylate/glycidyl methacrylate, the glycidyl methacrylate being grafted or copolymerized, PA1 polypropylene. PA1 polyethylene, polypropylene, ethylene-propylene copolymers, ethylene-butene copolymers, all of these products being grafted with maleic anhydride or glycidyl methacrylate. PA1 ethylene/alkyl (meth)acrylate/maleic anhydride copolymers, the maleic anhydride being grafted or copolymerized. PA1 ethylene/vinyl acetate/maleic anhydride copolymers, with the maleic anhydride being grafted or copolymerized. PA1 the above two copolymers in which the maleic anhydride is replaced with glycidyl methacrylate, PA1 ethylene/(meth)acrylic acid copolymers and optionally their salts, PA1 polyethylene, propylene or ethylene-propylene copolymers, these polymers being grafted with a product having a site which is reactive with amines; these grafted copolymers then being condensed with polyamides or polyamide oligomers having only one amine end. PA1 5 to 15% of an ethylene-propylene copolymer containing a predominant amount of polypropylene grafted with maleic anhydride and then subsequently condensed with monoamine oligomers of caprolactam. PA1 the remainder to 100% being polypropylene. PA1 5 to 15% of at least one copolymer of ethylene with (i) an alkyl (meth)acrylate or a vinyl ester of unsaturated carboxylic acid and (ii) an unsaturated carboxylic acid anhydride or an unsaturated epoxide which is grafted or copolymerized. PA1 the remainder being polyethylene. PA1 5 to 15% of polyethylene or copolymers of ethylene and of an alpha-olefin grafted with maleic anhydride or glycidyl methacrylate. PA1 the remainder being polyethylene. PA1 monomers having: PA1 an additive for improving the slip nature such as, for example, a fatty acid metal salt (zinc stearate), PA1 an antioxidant, such as, for example, a sterically hindered phenol, a mercaptan or a phosphite, PA1 ultraviolet radiation absorbers such as substituted benzophenones, substituted phenylbenzotriazoles and sterically hindered amines; extinguishers such as nickel complexes, inorganic or organic pigment, such as zinc oxide or titanium oxide.
Furthermore, between the PE and the PA, as between the EVOH and the PE, it is necessary to place a coextrusion binder or to introduce into the PE, the EVOH or the PA, a polymer having reactive groups in order to facilitate the adhesion of the various layers. Sachets manufactured with these multilayers are permeable to oxygen, and are therefore suitable for bleach.